The subject of the invention is a probe for an aircraft, making it possible in particular to measure the total temperature of the air flow surrounding the aircraft.
Measuring the total temperature is useful for determining the actual speed of the aircraft. What happens is that other sensors belonging to the aircraft are able to measure the total pressure Pt and the static pressure Ps of the aircraft. Knowledge of these two pressures Pt and Ps make it possible to determine the Mach number M of the aircraft, using the following formula:                     M        =                              5            ⁡                          [                                                                    (                                                                  P                        ⁢                                                  xe2x80x83                                                ⁢                        t                                                                    P                        ⁢                                                  xe2x80x83                                                ⁢                        s                                                              )                                                        2                    /                    7                                                  -                1                            ]                                                          (        1        )            
Incidentally, the Mach number M represents the ratio between the actual speed of the aircraft and the speed of sound. Now, the speed of sound, Vs, depends on the temperature, Ts, of the air surrounding the aircraft.
Vs={square root over (xcex3xc2x7rxc2x7Ts)}xe2x80x83xe2x80x83(2)
where xcex3 is a constant close to 1.4
r is the perfect gas constant
Ts is the static temperature of the air,
expressed in Kelvin.
The static temperature Ts is the temperature of the air at zero speed. This temperature is very difficult to measure on board an aircraft. It would be necessary to place a temperature sensor placed at the bottom of a hole more or less perpendicular to the skin of the aircraft in a region where the skin is more or less parallel to the air flow. This temperature sensor would in particular be disrupted by the skin temperature which would carry the risk of affecting the static temperature measurement. It is therefore preferable to measure the total temperature Tt of the air flow by placing the temperature sensor in the air flow. The static temperature Ts can then be determined using equation (3)
Tt=(1+0.2 M2)Tsxe2x80x83xe2x80x83(3)
All this makes it possible to determine the actual speed of the aircraft as a function of the total temperature Tt, the total pressure Pt and the static pressure Ps of the air flow surrounding the aircraft.
Total temperature measurement probes fixed to the skin of the aircraft are known. These probes plan for part of the air flow surrounding the aircraft to sweep over a temperature sensor. When the angle of incidence of the aircraft with respect to the air flow surrounding it is changed, the proportion of the air flow that sweeps over the temperature sensor is disrupted and this affects the total temperature measurement Tt. All this becomes increasingly important since it is when the aircraft is at a high angle of incidence that its speed needs to be known with precision.
The object of the invention is to improve the precision with which the total temperature Tt can be measured particularly when the angle of incidence of the aircraft with respect to the air flow surrounding it is high.
To achieve this objective, the subject of the invention is a probe for an aircraft, characterized in that it comprises a moving vane intended to orientate itself in the axis of an air flow surrounding the moving vane and, fixed to the moving vane, means for measuring the total temperature of the air flow.
In a particular embodiment of the invention, the following are grouped together in one and the same probe and fixed to a moving vane of the probe:
means for measuring the total temperature of the air flow;
means for measuring the total pressure of the air flow;
means for measuring the static pressure of the air flow;
means for measuring the angle of incidence of the aircraft.
Grouping these various measurement means together makes it possible to determine in a complete way the modulus and the direction of the aircraft velocity vector using a single probe. This grouping-together also makes it possible to reduce the number of openings made in the skin of the aircraft.